Since the development of the integrated circuit (IC), the semiconductor industry has experienced continued rapid growth due to continuous improvements in the integration density of various electronic components (i.e., transistors, diodes, resistors, capacitors, etc.). For the most part, these improvements in integration density have come from repeated reductions in minimum feature size, which allows more components to be integrated into a given area.
These integration improvements are essentially two-dimensional (2D) in nature, in that the area occupied by the integrated components is essentially on the surface of the semiconductor wafer. The increased density and corresponding decrease in area of the integrated circuit has generally surpassed the ability to bond an integrated circuit chip directly onto a substrate.
Different packaging techniques taking advantage of an additional dimension have been used to achieve various objectives. One package is a chip or chips on an interposer. Interposers have been used to redistribute ball contact areas from that of the chip(s) to a larger area of the interposer. Another development is the stacking of dies on an active die. This also allows for a package to include multiple chips and reduces the package footprint.
During processing, the interposer or bottom active die in these packages generally includes through substrate vias (TSVs, also referred to as “through semiconductor vias” or “through silicon vias”), and other dies are typically attached to the interposer or bottom active die before the interposer or bottom die is singulated from a wafer. After a die attach step, the wafer comprising the interposer or bottom active die is usually further processed, which typically includes various thermal processes. The coefficient of thermal expansion (CTE) or shrinkage of underfill can cause the wafer to warp during the thermal process. The warpage can impart a stress to the TSVs or other components of the package, such as an underfill material or bumps. The stress can cause cracks in the TSVs, cracks in the bumps, or delamination of the underfill material.